Assess toxicity and adverse side effects of this drug in these patients.

OUTLINE: This is a randomized, multicenter study. All patients initially receive the same dose of defibrotide IV over 2 hours every 6 hours on day 1. On day 2, patients are randomized to 1 of 2 doses of defibrotide.

Arm I: On days 2-14, patients receive a lower dose of defibrotide IV over 2 hours every 6 hours.

Arm II: On days 2-14, patients receive a higher dose of defibrotide IV over 2 hours every 6 hours.

In both arms, courses repeat every 14 days in the absence of disease progression or unacceptable toxicity.

PROJECTED ACCRUAL: A total of 140 patients (70 per treatment arm) will be accrued for this study.